The present invention is directed to the technology of high-density high-speed three-dimensional integrated circuits structures of silicon and gallium arsenide by localized epitaxial growth (LEG). Silicon dominates the high density circuits in LSI (large scale integration) and VLSI (very large scale integration) and gallium arsenide dominates the high speed circuit beyond 1 GHz. Also aluminum gallium arsenide can be combined with gallium arsenide to make electronic and optoelectronic gates with very high speed, low power and excellent noise immunity. The present invention shows apparatus and process for using all three in 3-D LEG, in which high quality single crystal GaAs is seeded by LEG silicon and epitaxially grown over an insulating barrier.
In the art it is known to grow epitaxial silicon inside the window of an insulator region such as is shown in Voss et al, "Device Isolation Technology by Selective Lowo-Pressure Silicon Epitaxy", 1983, IEDM, p35-38. An epitaxial lateral overgrowth of silicon over SiO.sub.2 is described by Jastrzebski et al, "Growth Process of Silicon over SiO.sub.2 by CVD:Epitaxial Lateral Overgrowth Technique", J. Electrochem. Soc., Solid-State Science & Technology, Vol.130, No.7, July 83, p1571-80. Yoshiro Ohmachi of NTT as reported the growth of GaAs on silicon by the use of a recrystallized germanium interface layer in Electronics, Dec. 15, 1983, p.85. This technique is unacceptable for the fabrication of lasers because of the high dislocation density which is inherent in a recrystallization technique. Inability to fabricate lasers makes it impossible to use the technique for high speed optical devices since LED's cannot be operated at the desired frequencies. The use of epitaxial germanium between silicon and gallium arsenide in large area silicon substrates is shown by Fletcher et al, "GaAs Light Emitting Diodes Fabricated on Ge-coated Si Substrates", App.Phy.Letters, 44(10), May 15, 1984, p967-69. The growth in a well described in this paper makes no mention of growing single crystal GaAs over the SiO.sub.2. Overgrowth of GaAs on the SiO.sub.2 allows the formation of GaAs devices which can be electrically isolated from the silicon substrate. This is particularly important for high speed GaAs electronics.
The present invention is directed to localized epitaxial structures of silicon, germanium and gallium arsenide (i.e. Al.sub.x Ga.sub.1-x As, where x.gtoreq.0) grown up through the window of an insulator layer such as SiO.sub.2 and then localized lateral epitaxial overgrowth of the GaAs over the surface of the surrounding SiO.sub.2, so that devices can be fabricated in the GaAs, or the GaAs can be used as a substrate for example AlGaAs/GaAs electronic and optoelectronic devices. The devices could be used for intra or inter chip communication involving GaAs MUX/DEMUX modules.